1. Field of the Invention
The present invention relates to a vehicle control device for engine control, transmission control, or the like for arithmetically processing a control amount according to a control program by using a microcomputer and, more particularly, to a vehicle control device in which a memory for storing a control program can be updated while being incorporated in the control device.
2. Description of the Related Art
Since a vehicle control device is generally under severe conditions such as temperature or vibration, a socket for attaching a ROM (Read-Only Memory) or the like for storing a control program cannot be used to improve vibration resistance in, especially engine control. For this reason, a program is written in the memory by an only-purpose machine before the control device is assembled, and the memory is directly soldered on a substrate.
For example, in an engine control device of vehicle control devices, the contents in a ROM may be necessarily changed due to unmatching between control data of respective engines in mass production or the like.
In this case, in a conventional technique, the ROM is once removed and updated, and then must be soldered. As a result, there are problems such as an increase in number of steps and degradation of reliability of the soldered portion.
In order to solve the above problems, in a conventional engine control device described in Japanese Patent Publication No. 8-2556562, in a change of the contents of a ROM, a new program is written in the ROM while the ROM is attached to a substrate.
However, such a conventional device has no measure about writing defect occurring in such a case that a signal is stopped due to some factor, e.g., an instantaneous cut-off operation of a line (communication signal line) in the middle of an updating operation. In steps following the writing operation, the ROM on which data is written by some method must be checked. For this reason, operation steps increase in number, and productivity is degraded. In addition, a check result may be overlooked by an artificial mistake in the check step.
In this case, when the above writing defect may appear as a control amount which is apparently abnormal under almost all operation conditions, overlooking in the check step may be detected in the following steps. However, when the writing defect may appears as a control amount which is abnormal under only a special condition, overlooking cannot be detected, and the defective products disadvantageously issue to the market.